“We would like to report that the Centers for Disease Control and Prevention have determined that the patient kept in isolation since Monday, August 4, 2014 at The Mount Sinai Hospital has tested negative for Ebola Virus Disease (EVD),” the hospital said in a statement. “The patient is in stable condition, is improving, and remains in the care of our physicians and nurses.”

It was not immediately clear what disease the man was suffering from. He had recently taken a trip to West Africa.

As WCBS 880’s Monica Miller reported, the CDC said so far, three Americans in the United States have been tested for the virus, and all of the tests have came back with negative results.

“New York is a major port of entry, so we have to remain vigilant,” Reich said.

Reich said the likelihood of seeing Ebola in New York City is greater than it would be in other American cities. “But I think our preparedness is also at a much higher level, so I think that should really reassure the public that people really are prepared to deal with health care threats in New York City,” he said.

Because disease control measures are much greater in the United States, an outbreak here would be extremely rare, Reich said.

The patient showed up to the Mount Sinai Medical Center emergency room Monday morning with a high fever and gastrointestinal problems.

The man was placed into “strict isolation” within seven minutes of his arrival, and was undergoing various tests to determine the cause of the symptoms, the hospital said.

Hospitals Across NYC Ready For Possible Ebola Cases

The Ebola virus causes a hemorrhagic fever that has sickened more than 1,700 people, killing more than 900, mostly in Liberia, Guinea and Sierra Leone.

It’s spread through direct contact with bodily fluids. A person exposed to the virus can take up to 21 days to exhibit symptoms, making it possible for infected travelers to enter the U.S. without knowing they have it.

The current outbreak is the largest since the disease first emerged in Africa nearly 40 years ago.

There is no cure or vaccine for Ebola, but a vaccine is set to begin human trials next month. So far, the vaccine has shown success in monkeys.